1. Field of the Invention
The present invention relates to a developing apparatus and an image forming apparatus provided with the same.
2. Description of the Related Art
Electrophotography, which can form high quality images easily, is widely used for image forming apparatuses such as copiers, printers, and facsimiles. Electrophotographic image forming apparatuses are generally configured including a photoreceptor drum containing photoconductive substances, a charging section, an exposure section, a developing section, a transfer section and a fixing section. The charging section uniformly charges the surface of a photoreceptor drum. The exposure section irradiates the charged surface of the photoreceptor drum with light based on image information to form an electrostatic latent image. The developing section supplies toner to the electrostatic latent image on the surface of the photoreceptor drum to convert the image to a visible image. The transfer section transfers the toner image carried on the surface of the photoreceptor drum on the surface of a recording medium. The fixing section fixes the toner image on the recording medium to the recording medium by heating, applying pressure or the like.
In general, a developing apparatus including a developing portion and a toner replenishing portion is used as the developing section. The developing portion is configured including a developing roller, a doctor blade, a stirring roller and a developing bath. The developing roller is provided in contact with the photoreceptor drum and includes a developing roller that carries a toner layer on its surface and supplies toner to an electrostatic latent image. The doctor blade is a plate-like member that abuts against the surface of the developing roller for regulating the thickness of the toner layer on the surface of the developing roller. The stirring roller charges toner by being driven to rotate and supplies the charged toner to the circumference of the developing roller. The developing bath that contains the developing roller, the doctor blade and the stirring roller and contains the toner. In the developing portion, the electrostatic latent image on the photoreceptor drum is converted to a visual image with the toner. Furthermore, the toner replenishing portion includes a toner hopper (or toner cartridge) and a toner transport pipe. The toner hopper is provided above the developing bath for storing toner. The toner transport pipe is provided between the toner hopper and the developing path so as to connect the two members, serving as a toner transport path for replenishing the developing bath with the toner in the toner hopper.
In the conventional image forming apparatus, when there is no more toner left even in the toner replenishing portion, only the toner hopper cartridge is replaced while the developing portion and the toner transport pipe remain as they are. In a portion of the toner hopper to which the toner transport pipe is attached, a toner replenishing port through which the toner is supplied to the toner transport pipe is provided, and further a shutter member for opening and closing the toner replenishing port is provided. The shutter member opens the toner replenishing port by attaching the toner hopper to the toner transport pipe. Therefore, at the same time when the toner hopper is attached to the toner transport pipe, the toner in the toner hopper is supplied to the developing bath through the toner transport pipe.
Such a shutter member can be used also in other apparatuses than the toner hopper, for example, in a toner reuse apparatus that has a toner receiving portion and a toner transporting portion and returns toner collected by a toner cleaner from the surface of the photoreceptor drum (see Japanese Unexamined Patent Publication JP-A 7-210048 (1995), for example) . Here, the toner receiving portion is supported by the developing bath and is provided with a toner receiving portion in its upper portion, and is provided such that the inner space of the toner receiving portion connecting to the toner receiving portion is in communication with the inner space of the developing bath. Furthermore, the toner transporting portion, which extends in the vertical direction, has an upper end portion and a lower end portion, and is a hollow member attachable to the toner receiving portion. A toner cleaner is connected to the upper end portion and a shutter member is provided so as to be a buttable against the toner receiving port in the lower end portion. In this toner reuse apparatus, when the toner transporting portion abuts against the toner receiving portion, the shutter member is opened abutting against the toner receiving port, and the inner space of the toner transporting portion is in communication with the inner space of the toner receiving portion via the toner receiving port, so that the toner falls from the lower end portion of the toner transporting portion and is supplied to the developing bath. When the toner transporting portion is separated from the toner receiving portion, the shutter member is not opened, so that the toner does not fall from the lower end portion of the toner transporting portion.
In the toner hopper and the toner reuse apparatus disclosed in the JP-A 7-210048, when the shutter member is opened, the toner in the toner hopper or the toner cleaner falls to the developing bath at once. Since toner is fine powder having a particle size of micron order, due to the reaction of falling, the toner leaks to the inside of the image forming apparatus from the portion in which the toner transport pipe is connected to the developing bath, a portion in which the toner transporting portion is connected to the toner receiving portion or other portions and scatters, and thus contaminates the inner portion of the image forming apparatus. The contamination in the inner portion of the image forming apparatus tends to cause poor image forming operation, defects in formed images, soil in unused recording media, high burden on maintenance and the like, and therefore there is a demand for reducing toner contamination.
Furthermore, at present, a developing apparatus employing a two-component developer containing toner and carrier is widely used while the life of the image forming apparatus is increased, resulting in a problem of long term durability of carrier filled in the developing bath of the developing apparatus, which necessitates replacement of a developing apparatus itself that is provided in the form of a cartridge. However, even when the shutter member is provided in a portion where the toner transport pipe abuts against the developing apparatus, toner may scatter and contaminate the inner portion of the image forming apparatus at the moment when the developing apparatus is detached from the toner transport pipe for replacement.
When the developing apparatus and the toner transport pipe is formed into one piece, toner can be preventing from scattering, but this requires significant labor and high cost for production, and is not suitable for industrial mass production.